Heat exchange unit and method of making same



Dec. 24, 1940.

F. B. HERZ' HEAT EXCHANGE UNI-1W ANDYMETHOD OF MAKING SAME Filed July18, 1938 Sheets-Sheet 1 INVEN TOR S m H n a A D m M m U D R E F Y B Dec.24, 1 940. F HERZ V 2,226,243

HEAT nxcmmgr: UNIT, D METHOD OF MAKING sum Filed July 18, 19:58sheets-sheet 2 INVENTOR FERDINAND B.H ERZ k 'BY I ATTORNEY Patented Dec.24, 1940 UNITED ,STATES poration of Illinois Application July 18. less,Serial No. 219,883

'1 Claims.

' headers in vertical'cross section;

Figure3isaplanview; Figure 4 is a sectional end elevation showin themethod of brazing the tubes to the headers. My improved heat exchangeunit is of the general type comprising a' plurality of series ofparallelly arranged tubes connected at their opposite ends to headersand having intermediate their ends a series of radiating fins spaced 25from each other to form air channels therebetween. It is one of theobjects of my invention to facilitate the assembly of such aunit so asto secure not only good thermal conductivity between the tubes and thefins, but also a joint between the tubes and headers of suflicientstrength to withstand the stresses to which the structure is subjected.It is usual to secure the fins to the tubes by soft solder which gives,the desired thermal conductivity, but this material is insumcient instrength to join the tubes to the headers, inasmuch as the latter maycontain steam under considerably higher than atmospheric pressure. Hardsolder such as various brazes, silversolder, etc, has the requisitestrength, but the temperature required for fusing it is much higher thanthe. fusing point of soft solder. It is necessary to assemble the finsupon the tubes and to'solder the same thereto before the tuba areassembled and secured to the headers, and consequently there is dangerthat in attaching the headers by hard solder this may loosen theconnection between the iins and tubes. It is one of the objects of myinvention to guard against this result as willbe hereinafter explained.

To secure high thermal conductivity the structure is preferably made ofcopper or bronze, the tubes being preferably formed from seamless drawncopper tubing and the headers made of cast metal. with suchconstruction,when Figure 2 is' an end elevation showing one of the lvrmrr OFFICE orcssm: r I

the unit is exposed to heat or pressure or the combination of heat andpressure, there is a tendency toexpand or distort in a manner to causestresses at the tube header joints, which would result in failure if notproperly guarded 5 against. This is due to the fact that the header isusually of a non-symmetrical form so that there is more 'or less warpingin the walls thereof. I have, however, avoided this defect by formingthe header with a central p'ortion which is substantially circular incross section and of 'a cylindrical form. This can be connected to thecentral row of tubes, while the outer row of tubes on opposite sides ofthe central row are connected to wings or lateral-extensions from thecentral portion. These extensions engage individual tubes of the seriesand leaves spaces therebetween in which'the header is of cylindricali'orm. Such shape permits use of exceptionally high pressures andtemperatures.

To eliminate the possibility of heating some of the tubes to a greaterextent than others by improving elimination of air,.and to insure properdistribution of steam. when unit is in service, 4 the ends of the tubemembers which form the 5 connection to the header are preferably reducedin size to produce a pressure loss at this point. This has the effect ofequalizing the amount of steam entering the several tubes to produce anq al heating effect. As

peciflcally" illustrated, A are the tubes preferably formedof seamlessdrawn tubing and which may be either of circular cross section or 7oval, if a streamline form is desired. B are the fins mounted on thesetubeswhich are provided 5 with the usual struck out flanges Bsurrounding the'apertures' through which" the tubes are passed andforming an extended surface for the soldered Joint. Preferably, thereare two or more parallel series of tubes which are em- 40 braced by thefins, and the joint is formed by iirst'tinning or coating the tubesiwithsolder, then placing the fins thereon in properly spaced relation, andthen heating the assembly to a temperature at which the solder will meltand form the joint. At op it'e ends of. the tubes A are headers C. Theseare formed with a central portion C which is bstantially cylindrical andto which the central row of tubes A are attached. Projecting laterallyfrom Opposite sides of this central portion are wing portions C eachengaging an individual tube of the outer series. The walls of thesewings merge into the cylindrical cross section' and the space betweensuccessive wings is sumcient to leave a considerable length of thecylindrical portion. There is also a nipple C for connecting with thesupply conduits, and one or more lugs C for attachment to the supportingstructure.

As before stated, there is danger in the attachment of the header to thetubes by hard solder that the heat may loosen the soft solder connectionbetween the tubes and the fins. This I have guarded against by placing arelatively heavy fin or plate D beyond the last of the thin fins andbetween the same and the ends of the tubes which are attached to theheader. The header is bored in registration with the tubes to permitinsertion of the latter and the hard soldering is then efi'ected in thefollowing man-. ner: Around each tube adjacent to the header is placed aring E of the hard solder. The header is then immersed in a heated bathpreferably of fused salt, which is maintained at a temperature highenough to melt the solder ring. The depth of insertion into the saltbath is such as to uniformly heat all of the walls of the header, butwithout directly heating the tubes. Also, the shield plate D which isabove the header will prevent radiant heat from the bath impingingagainst the fins. The time interval required for melting the solder iscomparatively short and such heat as is conducted upward through'thetubes will be largely absorbed by the shield plate D, so that thetemperature rise in the portions of the tubes soldered to the fins willnot be high enough to impair the fin to tube joint. Plate D serves theadditional purpose of shielding adjacent fins from the radiant heat ofthe bath, preventing excessive annealing of such parts. The fact thatall portions of the bath are at equal temperature, will cause theuniform heating of all of the tubes at the point of engagement thereofwith the header, so that the structure may be removed from the bath assoon as fusion occurs. It is, of course, understood that the joint issuitably fiuxed for this operation, to insure the union of the solderwith the header and tubes.

In first preparing the tubes A, the end portions A thereof arecontracted by suitable dies, so as to be of considerably smallerdiameter. These are the portions that aresoldered to the header whichreduces the amount of solder required. Also, the reduction in crosssectional area of the space within the contracted tubes, offers .arestriction to the flow of steam therethrough which will equalize thedistribution between the tubes.

What I claim as my invention is:

1. The method of forming heat exchange units comprising the assembly ofa plurality of series of tubes and fins sleeved-on said tubes to embraceall of said series, uniting said fins to said tubes by soft solder,engaging a shield with said tubes between the endmost fin and the endsof the tubes, placing rings of hard solder about each tube, engagingsaid tubes with registering apertures in a header, and immersing saidheader in a fused bath having a temperature suflicient to melt the hardsolder, said tubes projecting upward from the header and the soft solderjoints being protected from the heat of said bath by said shield.

2. The method of forming. heat exchange units comprising the assembly ofa plurality of series of tubes and fins sleeved on said tubes to embraceall of said series, uniting said fins to said tubes by soft solder,engaging a shield with said tubes between the endmost fin and the endsof the tubes, placing hard solder adjacent to each tube, engaging saidtubes with registering apertures in a header, and uniformly heating theends of said tubes and adjacent header for a. short interval to atemperature sufficient to melt the hard solder, the portions of saidtubes having soft solder joints being protected from destructive heatingduring said interval by said shield.

3. A heat exchange unit comprising a series of tubes, fins sleeved uponsaid tubes and embracing the entire series, the end portions of saidtubes beyond said fins being contracted in diameter to form asubstantial restriction of at least 50% in the area thereof, and aheader to which the contracted end portions of said tubes are attached.

4. In a heat exchange unit, a plurality of parallel series of tubes,fins sleeved on said tubes and embracing all of said series, a header towhich a heat absorbing and dissipating shield interposed.

between the finned portion of said tubes and said header for protectingthe soft solder joints and preventing the annealing of adjacent finsduring the hard soldering of said tubes to said header and also forminga permanent protection therefor.

6. A heat exchange unit comprising a. plurality of parallel series oftubes, fins sleeved upon said tubes and embracing all of said series, aheader having a substantially cylindrical central portion connected tothe central series of tubes, and integral spaced wing portionsprojecting laterally from said central portion and individuallyconnected to the tubes of the outer series, said fins having a softsolder connection with said tubes and said header a hard solderconnection therewith, and a plate of greater thickness than said finsinterposed between the latter and said header and forming a protectingshield.

7. A heat exchange unit comprising a plurality of parallel series oftubes including a central series and series on opposite sides thereof,fins sleeved on said .tubes and embracing all of said series, and aheader connected to the ends of said tubes, the openings from saidheader into said tubes being substantially restricted with respect tothe cross sectional area of the body of the tubes by at least 50% tocompel substantially uniform fiow' of fluid from the header into all ofthe tuba.

FERDINAND B. HERZ.

